Understanding Concurrency Issues in Java Networking

1. Networking • Server Socket waits for client connections and returns a dedicated socket for each new client

2. welcomingsocket clientsocket connectionsocket clientprocess serverprocess

3. Heap object of class Bob

4. Heap object of class Bob

5. Heap object of class Bob ‘Lock’

6. Heap object of class Bob ‘Monitor’

7. Race Condition

8. Race Condition Concurrency Problem병행성 문제

9. counter = 1 x = 2 class Bob { int counter = 1; void add_One { int x = counter + 1; .... .... .... .... counter = x; } } T1 counter = 2 T2 counter를 아직update 안 했어요! counter = 2

10. 없는대.. counter = 1 x = 2 counter = 2 counter = 2 x = 3 OK 잠깐 OK! 잠깐 ‘lock’ 어디 있니? ‘lock’ 어디 있니? class Bob { int counter = 1; synchronized void add_One { int x = counter + 1; .... .... .... .... counter = x; } } T1 T1 I’ll wait T2 T2 counter = 3

11. class Bob { int counter = 1; synchronized void add_One { int x = counter + 1; .... .... .... .... counter = x; } } T1 T2 T2 counter = 3

12. Class Locks T1 Bob synchronized void m1() void m2() static synchronized void m3() wait! T2

13. Class Locks T1 Bob synchronized void m1() void m2() static synchronized void m3() 됩니다! T2

14. Class Locks T1 Bob synchronized void m1() void m2() static synchronized void m3() 됩니다! T2

15. Class Locks T1 Bob synchronized void m1() void m2() static synchronized void m3() wait! T2

16. Finally T1 Bob synchronized void m1() synchronized void m2() wait! T2